Many industries may benefit from occupant detection systems and methods. One such industry is the transportation industry. For instance, several automotive applications are dependent upon an occupant or passenger being present in a vehicle. In one example, many airbag systems are only enabled when the passenger is in the seat. Generally, each airbag in the airbag system is associated with a specific passenger and seat. If a passenger is present in the seat, the airbag may be enabled. If no passenger is present in the seat, then the airbag remains disabled. However, studies have shown that normal airbag deployment may not be ideal, but deploying an airbag with reduced force or disabling airbag deployment under certain circumstances may be appropriate, especially when a small child or car seat is detected. Therefore, there are several instances where deploying an airbag is not ideal even though a passenger is detected. Accordingly, the airbag control system must be able to determine whether the passenger is an older child or an adult before enabling the airbag system. Other occupant detection systems used in other industries may need to make similar determinations.
Returning to the automotive example, previous airbag enabling systems have used proximity sensors to detect whether the person is present and enable the airbag system. The proximity sensors are able to detect the presence of nearby objects remotely by relying on the passenger to alter the effective dielectric between two plates of a capacitor. These proximity sensors may also determine the size of the passenger based on the capacitance. However, environmental conditions may interfere with the readings of the proximity sensor, resulting in false outputs. These false outputs may enable the airbag or other systems in an undesirable situation, such as when a small child or child seat is present. Specifically, environmental conditions may trick the sensor into determining that the passenger is larger than they actually are, or that enabling the airbag is otherwise appropriate. For instance, at least one of the environmental conditions may cause the sensor to detect a non-living object as a person. This could result in the sensor detecting shopping bags resting on a seat as a person and enable the airbag for that seat. Some environmental conditions that may cause false outputs include the humidity or other moisture inside the vehicle and the characteristics of the seat. Humidity affects the permittivity of the air, thus changing the flow of a charge between the person or object and the sensor. As seats age and foam in the seat compresses, the distance between the sensor electrode and the person may change, thus changing the capacitive coupling between the person or object and the sensor. There are other environmental conditions that may cause false outputs as well. In order to compensate for these and other environmental conditions, previous occupant detection systems employed multiple sensors, each detecting only one environmental condition.
Accordingly, an occupant detection system is needed that is able to detect occupants independent of the environmental conditions. Although the examples above were directed to airbag deployment in the automotive industry, the system may be useful in other automotive or non-automotive applications.